Port closures, such as a sliding sleeve, a gate, a mandrel, a valve, a detachable cover, a retainer holding the detachable cover in place, etc., are used in wellbore tubular strings and tools to permit selective opening of ports. The ports may provide fluid access between the annulus and the inner diameter of the tubing string or may provide fluid communication to and from a tool on the string, such as a packer.
Sometimes, although a port closure is actuated to open, it is desirable that the actual opening of the port to fluid flow be somewhat delayed.